Gene therapy using genetically engineered cells and viruses has undergone impressive development over the past 40 years. Gene therapy techniques have been applied to diverse medical problems and have been used in over 350 clinical trials (Wu et al., Meth. Strat. Anesthes. (2001) 94: 1119-1132). However, gene therapy has only recently been used in attempts to control pathological pain. Several approaches have been explored. For example, spinal implantation of genetically engineered cells has been used to increase inhibitory transmitters, including GABA (Eaton, M., J. Peripheral Nerv. Sys. (2000) 5:59-74), galanin (Eaton et al., J. Peripheral Nerv. Sys. (1999) 4:245-257), and beta-endorphin (Ishii et al., Exp. Neurol. (2000) 166:90-98). Herpes viruses have been utilized for their ability to be retrogradely transported from peripheral nerve terminals to dorsal root ganglion somas. In this way, elevations in preproenkephalin (Antunes Bras et al., J. Neurochem. (1998) 70:1299-1303; Wilson et al., Proc. Natl. Acad. Sci. USA (1999) 96:3211-3216) and decreases in CGRP via induced production of CGRP antisense (Lu et al., Soc. Neurosci. Abs. (1998) 24:1625) have been produced in sensory neurons. Lastly, adenoviruses have been injected into CSF to achieve virally driven beta-endorphin release from meningeal cells (Finegold et al., Hum. Gene Ther. (1999) 10:1251-1257. These gene therapy approaches focus on decreasing the excitability of spinal cord pain transmission neurons to incoming pain signals.
Activated spinal cord microglia and astrocytes appear to contribute to the creation and maintenance of pathological pain. In particular, activated glia appear to do so, at least in part, via their release of the proinflammatory cytokines interleukin-1 (IL1), tumor necrosis factor (TNF), and IL6 (for review, see Watkins et al., Trends in Neurosci. (2001) 24:450-455). These proinflammatory cytokines amplify pain by enhancing the release of “pain” neurotransmitters from incoming sensory nerve terminals and by enhancing the excitability of spinal cord dorsal horn pain transmission neurons (Reeve et al., Eur. J. Pain (2000) 4:247-257; Watkins et al., Trends in Neurosci. (2001) 24:450-455).
Astrocytes and microglia express receptors for IL-10 (Mizuno et al., Biochem. Biophys. Res. Commun. (1994) 205:1907-1915) while spinal cord neurons do not (Ledeboer et al., J. Neuroimmunol. (2003) 136:94-103). In vitro studies have shown that IL-10 can selectively suppress proinflammatory cytokine production and signaling in these glial cells (Moore et al., Ann. Rev. Immunol. (2001) 19:683-765). In fact, IL-10 is an especially powerful member of the anti-inflammatory cytokine family in that it can suppress all proinflammatory cytokines implicated in pathological pain (IL1, TNF and IL6). IL-10 exerts this effect by inhibiting p38 MAP kinase activation (Strie et al., Crit. Rev. Immunol. (2001) 21:427-449); inhibiting NFkappaB activation, translocation and DNA binding (Strie et al., Crit. Rev. Immunol. (2001) 21:427-449); inhibiting proinflammatory cytokine transcription (Donnelly et al., J. Interferon Cytokine Res. (1999) 19:563-573; inhibiting proinflammatory cytokine mRNA stability and translation (Hamilton et al., Pathobiology (1999) 67:241-244; Kontoyiannis et al., EMBO J. (2001) 20:3760-3770); and inhibiting proinflammatory cytokine release (Moore et al., Ann. Rev. Immunol. (2001) 19:683-765). In addition, IL-10 stabilizes mRNAs of Suppressors of Cytokine Signaling, thereby increasing the production of a family of proteins that further inhibit proinflammatory cytokine production (Strie et al., Crit. Rev. Immunol. (2001) 21:427-449). IL-10 also interrupts proinflammatory cytokine signaling by downregulating proinflammatory cytokine receptor expression (Sawada et al., J. Neurochem. (1999) 72:1466-1471. Lastly, it upregulates endogenous antagonists of proinflammatory cytokines, including IL1 receptor antagonist and TNF decoy receptors (Foey et al., J. Immunol. (1998) 160:920-928; Huber et al., Shock (2000) 13:425-434).
The known effects of IL-10 are restricted to suppression of proinflammatory functions of activated immune and glial cells, leaving non-inflammatory aspects of cellular functions unaffected (Moore et al., Ann. Rev. Immunol. (2001) 19:683-765). While some neurons express IL-10 receptors, the only known action of IL-10 on neurons is inhibition of cell death (apoptosis) (Bachis et al., J. Neurosci. (2001) 21:3104-3112). Laughlin et al. (Laughlin et al., Pain (2000) 84:159-167) reported that intrathecal IL-10 blocks the onset of intrathecal dynorphin-induced, IL1-mediated mechanical allodynia. These investigators then tested the effect of IL-10 on pathological pain induced by excitotoxic spinal cord injury, a manipulation that activates astrocytes and microglia at the site of injury (Brewer et al., Exp. Neurol. (1999) 159:484-493). IL-10 decreased pathological pain behaviors when given 30 minutes following injury (Plunkett et al., Exper. Neurol. (2001) 168:144-154; Yu et al., J. Pain (2003) 4:129-140). This is in keeping with the fact that systemic IL-10 can reduce spinal cord proinflammatory cytokine production in response to excitotoxic injury, a manipulation that allows systemic IL-10 to reach the injured spinal cord due to disruption of the blood-brain barrier (Crisi et al., Eur. J. Immunol. (1995) 2:3033-3040; Bethea et al., Neurotrauma (1999) 16:851-863).
However, delivery of IL-10 systemically to treat CNS disorders is problematic. IL-10 does not cross the intact blood brain barrier in appreciable amounts (Banks, W. A., J. Neurovirol. (1999) 5:538-555), has a short half life such that sustainable delivery for prolonged periods would be difficult (Radwanski et al., Pharm. Res. (1998) 15: 1895-1901), has not been successfully delivered orally, so presents problems for systemic administration, and would disrupt the normal functions of the body's immune system and would be expected to be detrimental to the health of the patient (Xing et al., Gene Ther. (1997) 4:140-149; Fedorak et al., Gastroenterol. (2000) 119:1473-1482; Tilg et al., J. Immunol. (2002) 169:2204-2209). Moreover, previous experimenters found that delivery of IL-10 24 hours after dynorphin-induced allodynia did not reduce the allodynia (Laughlin et al., Pain (2000) 84:159-167).
Previous reports have documented that IL-10 gene therapy reduced pneumonia-induced lung injury (Morrison et al., Infect. Immun. (2000) 68:4752-4758), decreased the severity of rheumatoid arthritis (Ghivizzani et al., Clin. Orthop. (2000) 379 Suppl.:S288-299), decreased inflammatory lung fibrosis (Boehler et al., Hum. Gene Ther. (1998) 9:541-551), inhibited cardiac allograft rejection (Brauner et al., J. Thoracic Cardiovasc. Surg. (1997) 114:923-933), suppressed endotoxemia (Xing et al., Gene Ther. (1997) 4:140-149), prevented and treated colitis (Lindsay et al., J. Immunol. (2001) 166:7625-7633), and reduced contact hypersensitivity (Meng et al., J. Clin. Invest. (1998) 101:1462-1467).
However, the ability of IL-10 gene therapy to reverse ongoing pain has not been documented prior to the present invention.